73-13 Experimental Rheology of Three-Phase Lava: Bubble Lives Matter

Session: Using Volcanic Deposits to Help Us Understand Volcanic and Magmatic Processes (Posters)

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Abstract:

Effusive basaltic eruptions, like the 2018 Kīlauea event, produce fast-moving, low-viscosity lavas that pose significant hazards. Lava rheology, which controls eruptive behavior, is primarily driven by melt composition, temperature, crystallinity and bubble content.  However, traditional viscosity measurements of crystallizing basalts often fail to account for all these factors, lacking the crystalline assemblage of natural samples and being typically bubble free.

To address this, we developed a new high-temperature, three-phase viscosity measurement technique (Halverson and Whittington, 2025). This method begins at subliquidus temperatures and uses shortened experimental durations to preserve original phenocrysts and a substantial portion of the original bubble population. Using samples from the 2018 Kīlauea, we conducted experiments at typical eruptive temperatures (1150−1105°C) and were able to retain bubble fractions of 20%-30%, i.e., the majority of the ~36% porosity in the starting material. Our results show significantly lower viscosities than those from traditional bubble-free experiments. Viscosities ranged from 116 Pa·s at 1150°C to a maximum of 1800 Pa·s at 1105°C, while traditional methods plateaued at approximately 14,000Pa⋅s at 1115°C. These results underscore that bubbles, depending on their size, shape, and abundance, have a far greater effect on viscosity than predicted by two-phase models developed on crystal-free suspensions.

Experiments were also conducted on samples from the Mauna Loa 1868 eruption, which are more vesicular (60±5%) and have a greater volume of large phenocrysts (~20% of the dense material). At 1175˚C, the effective viscosity was 84 Pas, with a 25% bubble fraction. At 1150˚C, the effective viscosity was 132 Pas, with a 50% bubble fraction. At 1125˚C, the effective viscosity increased to >100,000 Pas in under 60 minutes, indicating extensive groundmass crystallization at this temperature. The results from Mauna Loa will help us better understand how bubbles interact with crystals that are of similar dimensions.

In a continuation of this work, we conducted experiments with a controlled cooling ramp. We observed an unexpected initial decrease in viscosity during cooling, which then reverted to the expected trend of increasing viscosity after a few minutes. We tentatively propose that the initial viscosity decrease is due to the loss of spherical non-deforming bubbles prior to the onset of crystal growth. These non-deforming bubbles affect the bulk rheology in the same way as crystals, increasing the effective viscosity.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7437

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